1. Field of the Invention
The present invention relates to pumps and, more particularly, to a rotary viscosity pump.
2. Prior Art
U.S. Pat. No. 1,448,079 to Noeggerath discloses a viscosity pump with a rotary body having spiral grooves with both constant and varying depth. U.S. Pat. No. 1,448,080 to Noeggerath discloses a pumping body for viscosity pumps with curved pumping grooves. U.S. Pat. No. 3,762,313 to Schott, Jr. and French patent 2,478,222 disclose feeding screws with helical flights. U.S. Pat. No. 4,357,291 to Miller et al. discloses a screw with a radius of the screw root that changes along the length of the screw. U.S. Pat. No. 4,047,705 to Hanslik discloses a pair of axially tapered screws.
Viscosity pumps generally include a cylindrical rod turning inside of a fitted sleeve that causes material to move along the interface propelled by the shear between the sleeve and the surface of the rod. This type of pump is standardly used for high viscosity materials such as crude oil and plastics for injection molds. However, viscosity pumps include problems of low efficiency (requiring large motors), large size (none are currently available less than a foot long), and large compressed volumes which leads to poor time response.
There are no pump technologies today that combine the following characteristics: 1) small size (less than 2 cubic inches), 2) high temperature compatibility (450 degrees F.), 3) fast time response (less than 0.03 seconds to full pressure), 4) compatible with a wide range of viscosities (10 to 100,000 centipoise), and 5) low pressure variations during operation (less than 0.5% rms).